efee5258bc
The MPFR library is a C library for multiple-precision floating-point computations with exact rounding (also called correct rounding). It is based on the GMP multiple-precision library and should replace the MPF class in further releases of GMP. GCC >= 4.2 requires MPFR.
64 lines
1.7 KiB
C
64 lines
1.7 KiB
C
/* __gmpfr_ceil_log2 - returns ceil(log(d)/log(2))
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Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
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Contributed by the Arenaire and Cacao projects, INRIA.
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This file is part of the GNU MPFR Library.
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The GNU MPFR Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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The GNU MPFR Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
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http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
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51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
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#include "mpfr-impl.h"
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/* returns ceil(log(d)/log(2)) if d > 0,
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-1023 if d = +0,
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and floor(log(-d)/log(2))+1 if d < 0*/
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long
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__gmpfr_ceil_log2 (double d)
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{
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long exp;
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#if _GMP_IEEE_FLOATS
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union ieee_double_extract x;
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x.d = d;
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exp = x.s.exp - 1023;
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x.s.exp = 1023; /* value for 1 <= d < 2 */
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if (x.d != 1.0) /* d: not a power of two? */
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exp++;
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return exp;
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#else
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double m;
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if (d < 0.0)
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return __gmpfr_floor_log2(-d)+1;
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else if (d == 0.0)
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return -1023;
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else if (d >= 1.0)
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{
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exp = 0;
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for( m= 1.0 ; m < d ; m *=2.0 )
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exp++;
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}
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else
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{
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exp = 1;
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for( m= 1.0 ; m >= d ; m *= (1.0/2.0) )
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exp--;
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}
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#endif
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return exp;
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}
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